4. While conducting the tests on the 3-phase induction motor, the variation of rotational losses with respect to voltage can be obtained as
a)
b)
c)
d) View Answer

Answer: a
Explanation: Core loss is zero for , zero applied voltage but the friction and windage losses will be present in the machine which need to be overcome.

5. The external rotor resistance is
a) gradually cut out as motor picks up the speed
b) fixed for a stable point
c) removed instantalLy as the motor is started
d) added or reduced as per the efficiency requirementView Answer

Answer: a
Explanation: External resistance is gradually cut out after picking up the speed.

6. The speed of the squirrel-cage induction motor can be changed by varying slip.
a) True
b) FalseView Answer

Answer: b
Explanation: For squirrel-cage induction motor, the rotor get shorted and it can not be altered.

Answer: a
Explanation: As the speed practically remains constant and lesser than than the rated speed, it is similar to dc shunt motor.

8. If the squirrel-cage induction motor is replaced by a solid cylinder in an induction motor its slip will
a) increase
b) decrease
c) be same
d) zeroView Answer

Answer: a
Explanation: Reactance of the rotor will decrease as the leakage wil reduce, so the slip will increase.

9. Number of the slip rings required for the satisfied operation of an induction motor is
a) number of phases
b) number of poles
c) halve of number of poles
d) double the phasesView Answer

Answer: a
Explanation: Slip rings number is same as the phase of the supply.

10. I. An induction can never operate at leading power factor.
II. Speed of the induction motor can be made more than synchronous speed and still it will work as motor.
a) I is true, II is false
b) I is true, II is true
c) I is false, II is true
d) I is false, II is also falseView Answer

Answer: a
Explanation: Speed more than Ns will be an induction generator not motor.